arXiv Machine Learning By Liv G. d'Aliberti, Marwa Abdulhai, Sofiia Druchyna, Peter Henderson, Manoel Horta Ribeiro

Measuring and Mitigating Solution Mode Collapse in RLVR

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The paper introduces ModeBench, a benchmark for multi-solution tasks that evaluates both correctness and the diversity of solutions found by a language model. It shows that reinforcement learning with verifiable rewards (RLVR) tends to collapse solution modes, concentrating probability on fewer correct answers even while accuracy remains high. To counter this, the authors propose Re:Max, a replay-based method that stores one verified example per discovered mode and trains uniformly on these stored modes, improving both success rates and solution diversity across various model scales and RL objectives.

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